Electron gun structure



2 Sheets-Sheet 1 Filed May 28, 1963 V w M y) W5 A April 19, 1966 OESS ELECTRON GUN STRUCTURE 2 Sheets-Sheet 2 Filed May 28, 1963 f w M M J z /0 IJA 0. Z 5 w a w y 5 United States Patent 3,247,410 ELECTRON GUN STRUCTURE Frederick G. Oess, Oceanside, Calif., assignor to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Filed May 28, 1963, Ser. No. 283,837 6 Claims. (Cl. 31378) This invention relates to electron discharge devices especially of the type employing an electron beam for scanning a target electrode therein. More particularly, the invention relates to an electron gun for forming a high precision electron beam for target scanning purposes.

Scanning electron beams are utilized for many purposes in various cathode ray tubes. The general purpose is to provide either an electrical or visual response in point-to-point fashion upon a target electrode by scanning the target electrode in point-to-point fashion with a fine pencil-like beam of electrons. Thus, in cathode ray tubes for television or radar-type visual displays the target electrode is a viewing screen composed of a layer of phosphor material which is excited to luminescence upon impingement thereon of electrons. In signal or frequency conversion tubes the target electrode may be composed of a material which responds electrically to impingement of electrons thereon as by emitting more electrons therefrom (called secondary electrons) than the number of electrons arriving thereat (called primary electrons) in the scanning electron beam. In some cathode ray tubes this phenomenon of secondary electron emission is utilized to form a pattern of electrical charges on a target which pattern is capable of being retained for substantial periods of time and which can be later read-out by subsequent re-scanning with an electron beam as a stored or delayed electrical signal. Alternatively, it is common in some tubes to utilize such a pattern of stored electrical charges to control the passage of other electrons, called flood electrons which blanket the storage electrode, through the target electrode so that a stored visual display may be provided. In still other instances the conductivity of a target electrode may be altered at will in response to bombardment thereof by a scanning electron beam. This phenomenon of bombardment induced conductivity is utilized in a visual display tube to provide visual displays in response to one or more scanning electron beams which displays may be non-stored (live) as well as stored. In addition, in such tubes the stored displays are capable of being selectively erased or replaced under control of a scanning electron beam. Such a tube is described in US. Patent 3,086,139 to N. H. Lehrer assigned to the instant assignce.

' In such tubes it will be appreciated that the ability to form precise and accurately controllable electron beams is extremely critical. In the selective erasure tube referred to above, for example, it is absolutely necessary that the erasing beam be able to return time and time again to exactly the desired portions of the storage target, else portions of the storage pattern which should not be altered will be altered and portions which should be altered will remain unaifected. Where such tubes are used in controlling the firing and guidance of missiles, for example, imprecise beam scanning can Well be the difference between success and failure.

The accuracy and reproducibility of a scanning electron beam are, of course, determined in large part by the electron gun structure itself. As used herein the term electron gun normally means that structure for generating and forming electrons into a pencil-like beam of relatively small cross-section. However, in some instances where positioning of the beam is accomplished by has been obtained the electrode elements are then welded' 3,247,410 Patented Apr. 19, 1966 phrase is therefore intended to include such deflection plates when applicable, although the invention is by no means limited to such combination but may be practiced to advantage in tubes utilizing magnetic deflection. Such gun structures involve a number of parts or electrodes which must be maintained at proper potentials in order to form an electron beam of the desired penoil-like character. In general, most electron guns comprise, in the order named, a control electrode adjacent an electron source or cathode, a first anode with a limiting aperture therein, a focusing electrode, and a final anode. The functions of these electrodes will be described in greater detail hereinafter; sufiice to say at this time is that different electrical potentials, some of great magnitude, must be maintained on the various gun elements and these elements must be very precisely and accurately aligned. Heretofore, it has been customary to secure the various gun elements to glass support rods extending along the gun axis and outside of the gun structure itself, the gun elements being hung or supported by transversely extending rods or pins welded to the gun elements and embedded in the glass support rods. A typical electron gun structure of this nature is shown in US. Patent No. 3,008,064, for example. In assembly the gun parts are arranged and aligned and one by one secured to the glass support rods by heating these rods so as to permit embedding the pins into the yieldable glass rods while maintaining alignment. It will be appreciated that maintaining the necessary alignment during such assembly and heating is rather diflicult; a subsequent heating step for one part may easily undo a previously secured part or cause a strain or stress therein which will result in mis-aligning such previously secured parts. In addition, such gun structures are fragile and must be handled with great care to avoid physically moving the glass support rods in any way else alignment of parts will be lost.

It is, therefore, an object of the present invention to provide an improved electron gun.

Another object of the invention is to provide an improved electron gun of high precision.

Another object of the invention is to provide an improved electron gun of rugged and rigid construction.

Still another object of the invention is to provide an improved electron gun of rugged and unitized construction and of high precision.

Yet another object of the invention is to provide an improved electron-gun of simple yet rugged and precise construction.

Another object of the invention is to provide an improved electron gun with superior alignment accuracy.

Still another object of the invention is to provide an improved electron gun in which electrical charging of insulator structures and supports is minimized with the resultant minimization of electron beam distortion.

These and other objects and advantages of the invention are realized by providing an electron gun structure in which electrode elements to be maintained at the same potentials are welded to one another while those electrode elements which must be maintained at different potentials are welded to an insulated three-point suspension system comprising short metal rods or pins embedded in glass or other electrically insulating headers extending between the electrode elements. In assembly, all of the electrode elements are mounted on a mandrel which extends longitudinally through the elements and the apertures therein through which the electron beam is designed to pass. After substantially perfect alignment into position to yield arugged, rigid and utilized structure of superior alignment accuracy.

The invention will be described in greater detail by reference to the drawings in which:

FIGURE 1, is an elevational view in section of an electron gun structure according to the invention;

FIGURE 2 is a right-hand end view of the electron gun structure shown in FIGURE 1;

FIGURE 3 is an elevational view of an electron gun according to the invention including electron beam defiection plates; and

FIGURE 4is an elevational view of the electron gun and beam deflection plate structure shown in FIGURE 3 turned 90 with respect to the view in FIGURE 3.

Referring now toFIGURES 1 and 2, an electron gun 1 embodying the principles of the invention is shown comprising a control electrode 2, a first anode electrode 4, a limiting aperture electrode 6 (which is normally considered a part of the first anode, at least electrically), a focusing anode 8, and a final anode 10, all of cylindrical shape in cross-section. A cathode assembly 3 is shown disposedwithin the control electrode 2 according to conventional techniques and comprises a cathode cylinder or sleeve containing cathode material 7 on the end thereof and a resistance heating element or filament 9 therewithin. As suggested, the cathode assembly may be of any conventional design and the mounting thereof in the electron gun 1 maybe according to practices well known in the art.

The control grid 2 comprises a metallic cylinder having an open and a closed end and adapted to receive the cathode assembly 3 and its electrical connections through the open end thereof with the electron emitting portion 7 adjacent the closed end which is provided with a centrally disposed aperture 11 in alignment with the cathode assembly 3. In practice, the cathode 3 may be operated at a potential of about 3 kv. negative, for example, with respect to ground. The control electrode 2 may be maintained at a potential from to 80 voltsnegative with respect to the cathode potential. The electrode 2 is called a control electrode because itis adapted to have its potential modulated in accordance with signals applied thereto to regulate or control theintensity of the electrons passing through the aperturel-l thereof.

Adjacent the closed end of the control grid 2 is the first anode electrode 4 comprising :a metallic cylinder having a closed end containing a centrally-disposed aperture 13 adjacent to and in alignment with the aperture 11 in the control grid 2. Theother end of the first anode 4 is provided with an outwardly extending lip or flange 15 for a purpose to be more fully described her inafter. In practice the first anode 4 may be operatedat a potential of from 50 to 100 volts positive, for example, with respect to ground in order to accelerate and converge the electrons passing therethrough into a high velocity beam.

Disposedand extendingwithin the open end of the first anode 4 is a thimble-like aperture-forming element 6 likewise having a centrally apertured closed end which extends into the first anode .4 The other end of this element v 6, which may be called the limiting aperture element, is provided with an outwardly extending lip or flange 17 adapted to be welded to the flanged portion 15 of the firs t anode 4. The aperture 19 in theclosed end of the electrode 6 is intended to intercept fringe or peripheral electrons in the beam being formed so as to limit the cross-sectional area of the beam as desired.

Coaxially disposed adjacent the limiting aperture electrode 6 is the focusing electrode 8 in the form of an open-ended metallic cylinder. The means for mounting and supporting this cylinder 8 will be described in greater detail hereinafter. The focusing anode may be operated at a potential of about 2.3 kv. negative, for example, with respect to ground in order to focus the electro beam therein.

The final electrode or anode 10 is provided with a closed end having a centrally-disposed aperture 21 and an open end disposed adjacent the open end of the limiting aperture electrode 6 in back-to-back fashion. The final anode 10 comprises a metallic cylinder having two integral portions of different dimensions, the larger portion 23 being intended to contain the focus anode 8. The open end of the final anode 10 is provided with an outwardly extending flange 25 adapted to be welded to the flanged portion 17 of the limiting aperture electrode 6. It will be understood that the final anode 10 and the first anode 4 as well as the limiting aperture electrode 6 are all operated at the same potential and may thus be physically and electrically connected together by the welding of their respective flanged portions. It will also be understood that the control electrode 2 and the focus anode 8 are operated at different potentials and must therefore be electrically isolated from each other and the other electrode portions of the electron gun. It has, therefore, not been deemed practical heretofore to attempt to provide these electrodes into a unitize-d assembly or one wherein the electrodes are physically connected to each other.

According to the embodiment of the invention shown in FIGURE 1 the control grid 2 is physically connected to and supported by the first anode 4 by means of brackets such a the bracket 27 which is welded to the first anode 4- and extended upwardly and over the control grid 2. Where physical support of the control grid is to be achieved by such a bracket arrangement it is preferred to employ three such brackets positioned apart around the first anode to facilitate and enhance alignment and rigidity of the control grid with respect to the first anode.

The end of the bracket 27 which extends over the control grid 2 is provided with an aperture in which is disposed an electrically insulating header assembly 29 containing 21 pin or rod 31 extending therethrough. to contact the outside of the control electrode 2. In practice, the header assembly comprises an outside metallic collet 33 "having a flanged portion or rim which is welded to the bracket 27. Within the collet 33 is an electrically insulating material 35 such as ceramic which may be fused to the collet 33 and to a sleeve member 37 extending through the ceramic portion 35. A similar header assembly 39 is also provided in and through the wall of the larger portion 23 of the final anode 10 so as to position and sup port the focus electrode 8. The sleeve member 37 may be omitted if a reasonably close fit between the ceramic header portion 35 and the pin 31 extending therethrough can be conveniently provided.

In assembly, the focus anode 8 is centered and aligned as desired within the final anode 10 by any suitable mandrel or jig arrangement. Pins 31' are then dropped through the sleeve members 37' in the header assemblies 39 which may be positioned 120 apart through the wall of the final anode 10. The pins 31' are then welded to the wall of the focus anode 8. The limiting aperture electrode 6 may then be mounted and aligned in place by welding its flange portion 17 and the flange portion 25 of the final anode 10 together. It is also possible to position and align the first anode 4 into place at the same time and weld its flange portion 15 to the flange portions 17 and 25 by one welding operation. The control electrode 2 is then positioned and aligned on the mandrel or jig assembly with the first anode 4 and the pins 31 are dropped into place through the header assemblies 28 and welded to the wall of the control grid 2. In this manner the electrode members of an electron gun are physically connected together to form a unitized assembly while achieving the requisite electrical isolation. It will also be appreciated that all parts or electrodes may be mounted and maintained in alignment as desired until the final weld is made. i In addition the pins 31 supporting the focus anode 8 and the control grid 2 serve admirably for making the desired electrical connections to these electrodes from outside of the completed structure and after fabrication of the electron gun. Often it was necessary in the prior art techniques using glass side support rods to provide such connections during or prior to assembly because of subsequent inaccessibility of the electrodes. This is particularly true with respect to the focus anode 8 which is Wholly contained with and between the final anode 10 and the limiting aperture electrode 6. Furthermore, it will be noted that those electrodes which are mounted by the header-pin assembly may be considered to be floating. In the case of expansion of the control grid 2, for example, due to the heat required in the cathode structure 3, the control grid can expand freely and yet remain in alignment.

It will be understood that other shapes and configurations of the electron gun structures just described are feasible and may be utilized to equal advantage. Thus, the first anode 4 may be provided having a greater diameter than that of the control grid and having the aperture 13 formed in a thimble-like cylinder (corresponding to the limiting-aperture element 6) which is recessed into the end of the anode cylinder. The end of the anode cylinder 4 may then be extended over the end of the control grid 2 and secured thereto by header-pin assemblies 29 as described previously so as to eliminate the need for extra brackets such as the bracket 27, for example.

Referring now to FIGURES 3 and 4, the electron gun assembly 1 of the invention is shown with an electrostatic deflecting plate system 40 to demonstrate how the unitized gun assembly lends itself to further rugged unitization and accurate alignment with other components and mounts in a cathode ray tube. The deflecting plate system 40 comprises a pair of vertical deflecting plates 42 and a pair of horizontal deflecting plates 44. The horizontal deflecting plates 44 are secured to and between a pair of frame support plates 46 and 48 by means of a header-pin assembly 29 as utilized in connection with the electron gun structure described previously. Since the deflection plates are planar and must be supported directly by these header-pin assemblies, the sleeve elements 37 are desirable in order to provide firm and substantially unmovable support for the pins 31 extending therethrough which might not otherewise be so readily obtainable. The support plate 46 is longer than the support plate 48 so that while these plates are co-terminous at one end, the other end of the support plates 46 extends further in the direction of the axis of the electron gun assembly 1 than the corresponding end of the support plate 48. This arrangement permits the end of the support plate 46 to be welded to a bracket member 47 which is welded to the ouside of the first anode member 4 of the gun assembly. The corresponding but shorter end of the frame support plate 48 is also welded to the lower end of the mounting plate 41 which is in turn welded to the first anode member 10 as shown in FIGURE 1. The upper end of the mounting plate 41 may likewise be welded to a tab portion (not shown) in the upper support plate 46 for further rigidity. Side plates 50 and 50' for mounting the vertical deflecting plates 42 are then Welded to the side portions of the frame support plates 46 and 48.

The vertical deflecting plates 42 are mounted between the side plates 50 and 50 by the previously described header-pin assemblies 29', three such assemblies spaced approximately 120 apart being utilized for this purpose with the pins 31 thereof being welded to the deflecting plates and to the sleeve members 37 as best shown and labelled in FIGURE 1. The horizontal deflecting plates 44 are mounted between the co-terminous plate portions of the support plates 46 and 48 by correspondingly disposed header-pin assemblies 29. Between the vertical and horiozntal deflecting plate systems 42 and 44 an interplate spacer 43 may be provided having an aperture therein to permit passage of the electron beam there through. This inter plate spacer 43 may be welded to the ends of the plates 50 and 50 of the frame support assembly in order to add greater rigidity and ruggedness to the structure, while shielding the deflection plate systems from each other. While the vertical deflecting plates 42 have been shown as adjacent the electron gun assembly 1 and mounted between the side plates 50 and 50 which in turn are affixed to the support plates 46 and 48, it will be understood that such arrangement is not necessarily the only one possible; that is, the horizontal deflecting plates 44 may just as conveniently be mounted adjacent the gun assembly 1 and between the side plates 50 and 50' with the vertical deflecting plates 42 being mounted where the horizontal deflecting plates 44 are shown. Also, it is feasible to mount the vertical deflecting plates adjacent the gun assembly 1, as shown, but secure these plates to the support plates 46 and 48 rather than to the side plates 50 and 50 which would then be used for supporting the horizontal deflecting plates 44. It should also be appreciated that any of the header assembly pins 37 may be utilized as electrical connections for applying desired deflecting potentials to the deflecting plates.

While a frame support system for the deflection assemblies 42 and 44 has been described utilizing frame support plates 46 and 48 having side plates 50 and 50 welded thereto, it will be appreciated that other support techniques and arrangements are feasible. Thus an integral three-wall U-shaped frame member may be used, the fourth wall or side plate being welded into position after mounting and securing the deflection systems there- 1n.

By the arrangement and structures shown and described it is thus possible to provide an extremely rugged electron gun assembly either alone or in combination with an electrostatic deflecting plate system. The electron gun as well as such combinations therewith are unitized with a minimum number of parts While also providing the necessary electrical isolation of the different electrodes with a minimum amount of electrical isolating materials such as glass and the like. Further, almost all of the fabricating and mounting procedures can be performed on conveniently available externalsurfaces of the assemblies thus permitting the use of internal mandrels and the like for securing accurate alignment of the components.

What is claimed is:

1. An electron gun assembly for a cathode ray tube comprising: first, second, and third cylindrical electrode members successively disposed about a common axis; a fourth cylindrical electrode member concentrically disposed within said third electrode member; said second and third electrode members being secured together in electrically conductive relationship; said first and fourth electrode members being secured to said second and third electrode members, respectively, by electrically conductive radially-extending pin members mounted in electrically conductive relationship to the outside surfaces of said first and fourth electrode members; and pin members extending into portions of said second and third electrode members and being electrically insulated therefrom.

2. An electron gun assembly for a cathode ray tube comprising; first, second, and third cylindrical metallic electrode members successively disposed about a common axis; a fourth cylindrical metallic electrode member concentrically disposed within said third electrode member; said second and third electrode members being secured together in electrically conductive relationship and having apertured portions; radially-extending metallic pin members secured to the outside surfaces of said first and fourth electrode members and extending into the apertures of said apertured portions of said second and third electrode members, respectively; and means disposed in said apertures of said apertured portions of said second 7.- and third electrode members for electrically insulating saidpin member therefrom.

3 The invention according to claim 2 wherein said first and fourth electrode members each have at least three of said pin members secured thereto and spaced surfaces of said first and fourth: electrode members; saidpin members extending'into portions of said-second and third electrode member'sand beingfielectrically insulated therefrom; a support structure secured to at least one of said electrode members and extending-beyond said third electrode member inthe direction of said common axis; and electrostatic deflecting plate members disposed about said common axis and mounted to and within said support structureby metallic pin members secured to said deflecting plate members in electrically conductive relationship; said last-named pin members extending into portions'of said "support structure andbeing electrically in-.

sulated therefrom.

5. An electron gun assembly for acathode ray tube comprising: a cylindrical control electrode member; a.

first anode cylindrical electrode member disposed adjacent said control electrode member; a second anode cy-- lindrical electrode member disposed adjacent and secured to said first anode electrode member in electricallyconductive relationship; a cylindrical focussing electrode member concentrically disposed within said second anodev electrode member; all of said electrode members having, a common axis; electrically insulating header means disposed in portions of said first and second anode electrode members; radially-extending electrically conductive.

pin members secured to said control electrode member in electrically conductive relationship therewith and extending through said header members in said first anode electrode member; and electrically conductive radiallyextending pin members secured to said focussing-electrode member in l tri ally conduc ive relationship.

in said second anode electrode member.

6. An electron gun assembly for acathode ray tubecomprising:. a cylindrical control electrode member; a first anode cylindrical electrode member disposed adjacent said control electrode member; a second anode cylindrical electrode member disposed adjacent and secured to said first anodeelectrode member in electrically conductive relationship; a cylindrical focussing electrode member concentrically disposed within saidsecond anode electrode member; all of said electrode members having a common axis; electrically insulating header means disposed in portions of said first and second anode. electrode members; radially-extending electrically conductive pin members secured to said control electrode member in electrically conductive relationship therewith and extending through said header members in said first anode electrodemember; electrically conductive radially-extending pin'members'securedto said focussing electrode member in electrically conductive relationship therewith and extending through said header members in said second anode electrode member; a frame support member secured to saidfirst and second anode electrode members and extendingbeyond said secondanode electrode member in the directionof said common axis; electrically insulating header means disposed in said frame support member; electrostatic deflection plate members disposedabout said common axis and having electrically conductive pin-mem'berstsecured thereto in electrically conductive relationship; said pin members secured to said deflection plates extending through respective said header members in said framevsupport member.

References Cited by the Examiner UNITED STATES. PATENTS 2,161,437 6/1939 Sprague et a1. 313-82.1 2,407,708 9/1946 Kilgore et al 3155.27 X 2,947,897 8/1960 Rodriguez et al. 31382.1 3,142,799 7/1964 Wendt 3l380 X FOREIGN PATENTS,

802,108 10/1958 Great Britain;

DAVID J. GALVIN, Primary Examiner. GEORGE N. WESTBY, Examiner.

R. .JUDD, Assistant Examiner. 

1. AN ELECTRON GUN ASSEMBLY FOR A CATHODE RAY TUBE COMPRISING: FIRST, SECOND, AND THIRD CYLINDRICAL ELECTRODE MEMBERS SUCCESSIVELY DISPOSED ABOUT A COMMON AXIS; A FOURTH CYLINDRICAL ELECTRODE MEMBER CONCENTRICALLY DISPOSED WITHIN SAID THIRD ELECTRODE MEMBER; SAID SECOND AND THIRD ELECTRODE MEMBERS BEING SECURED TOGETHER IN ELECTRICALLY CONDUCTIVE RELATIONSHIP; SAID FIRST AND FOURTH ELECTRODE MEMBERS BEING SECURED TO SAID SECOND AND THIRD ELECTRODE MEMBERS, RESPECTIVELY, BY ELECTRICALLY CONDUCTIVE RADIALLY-EXTENDING PIN MEMBERS MOUNTED IN ELECTRICAL- 